Answer:
multiple and divide are depending on the powers ( sometimes the numbers before the scientific n.)
 If the power neg- , it's going down 
like this 10^-5 = 1/10^5
 If the power pos+ , it's the same idea but different in signs .
Adding and subtracting are depending on numbers ( If the scientific n. is the same number) .
for example: 
3x10^5 + 4x10^5 = (3+4)x10^5 = 7x10^5 
 
        
             
        
        
        
Answer:
the third one
Step-by-step explanation:
the third one
 
        
             
        
        
        
Answer:
 irrational because the square root of 51 is irrational.
 
        
             
        
        
        
Answer:yes
Step-by-step explanation:
It's because both ways means the same due to the presence of positive sign.if the signs changed,it means that they are not the same